1. Field of the Invention
This invention relates to a compact four-unit five-lens behind diaphragm lens having an angle of view of 60.degree. or greater and brightness of the order of F2.8.
2. Description of the Prior Art
Generally, as a behind diaphragm lens having brightness of the order of F2.8, use is made of a Tessar type lens or a modified type thereof. In the Tessar type, if the focal length of the lens system is f, aberrations are well corrected when the length from the fore end to the image plane or surface (the total length of the lens) is of the order of 1.15f.
In contrast, in a type wherein the direction of the cemented surface of a cemented lens of the Tessar type having its convex surface facing the object side is reversed and the first lens of the cemented lens is a positive lens and the second lens of the cemented lens is a negative lens and a positive meniscus lens of a first unit is divided into two positive lenses, the total length of the lens can be shortened to the order of 1.08f and therefore, such type is used as a compact lens. A four-unit five-lens behind diaphragm lens of this type is known from Japanese Laid-open Patent Application No. 30027/1979 or No. 39510/1981, but generally, as regards the off-axis light beam, coma and chromatic coma of a light ray passing through the vicinity of a center of the diaphragm, namely, a light ray entering from the underside, tend to remain saliently, and this has led to an insufficient depiction.